Re: Why does this work in matlab and not PDL?

Ok, first of all I must apologise I realise now one of matrix dimensions were incorrect.

Anyway ... given the matrices
A = 71 x 35
B = 35 x 35
C = 35 x 7
D = 7 x 7
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The matrix multiplication should be I hope

(71x35) x (35 x 35) x (35 X 7) x (7 x 7)
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 A x B x C x D
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But it doesnt work. Any suggestions much appreciated.

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Re^2: Why does this work in matlab and not PDL? by Roy Johnson (Monsignor) on Sep 20, 2005 at 14:13 UTC
Have you tried breaking it up into one multiplication at a time? `$X = $A x $B; $X = $X x $C; $X = $X x $D;` [download] That should tell you (at least) which of the multiplications PDL thinks has the wrong dimensions. Is it possible to have PDL tell you what dimensions it thinks each variable has? Caution: Contents may have been coded under pressure.	[reply] [d/l]
Re^3: Why does this work in matlab and not PDL? by thor (Priest) on Sep 20, 2005 at 14:47 UTC
This shouldn't be necessary. Matrix multiplication is associative, meaning that A x (B x C) == (A x B) x C, so it really shouldn't matter in which order PDL is evaluating the multiplications. However, given that there is an error at all would suggest that there's something else going on and I do agree with your approach to debugging it. :) thor `Feel the white light, the light within Be your own disciple, fan the sparks of will For all of us waiting, your kingdom will come`	[reply]